1. Field of the Invention
The present invention relates to a cellular mobile communication system. Particularly, the invention relates to a mobile communication system that communicates with a mobile terminal within a cell using a single frequency.
2. Description of the Related Art
According to a conventional cellular mobile communication system, divided into n cells to avoid radio interference with adjacent cells. The same frequency band is repeatedly used in each of the n cells, thereby avoiding radio interference with adjacent cells. However, according to this system, a frequency band that can be simultaneously used in adjacent cells becomes 1/n, and a satisfactory communication speed cannot be obtained.
In this case, when the same frequency is used in adjacent cells, a terminal near a base station that is positioned at the center of a cell can communicate with other terminal, without receiving radio interference from other station. However, a terminal positioned far from the center of the cell cannot communicate satisfactorily with other terminal, because of radio interference from the adjacent cells.
Therefore, according to a conventional technique, in a cellular communication using a time division multiple access (TDMA) system, frequency utilization efficiency can be improved by allocating a channel to an idle time slot, as disclosed in Japanese Patent Application Unexamined Publication No. 11-88939, for example.
However, in the above example, the technique is limited to the use of a time slot according to the TDMA system, and the technique cannot be applied to a more general cellular communication system such as a frequency division multiplex access (FDMA) system.